Method for production of graph scale of cathode-ray tube panel for a oscilloscope

ABSTRACT

A method for production of graph scales of a panel of a cathode-ray tube for an oscilloscope for forming the panel graph scales by exposing and developing a slurry precipitate on a panel through a mask having cathode scales. More particularly, the present invention relates to a panel graph scale production method of a novel type characterized in that a specific filter having light transmissivity of about 62% at the center is disposed between the mask and a light source. According to this method, it is not necessary to arrange a large number of parallel ray lenses between the mask and the light source as opposed to the prior art, the distance between the panel and the light source can be more reduced, the overall exposure system for producing the scales can be more simplified, and the intended panel graph scales can be produced under an ideal condition.

BACKGROUND OF THE INVENTION

The present invention relates to a new method for forming graph scaleson the panel of a CRT for oscilloscope, in method for forming graphscales on the panel by Exposition & Development System beingcharacteristic of placing between a negative mask for the graph scalepatterns and a light source a specific filter whose light transmissivityat its center is about 62% and gets larger along from its center to itsperipheral portions.

In general, for example as shown in FIG. 1, the graph scale patternsincluding the scales for graph coordinates 1 and other necessarynumerical values 2 are drawn on the surface of the panel(P) of the CRTfor a oscilloscope. In the past, these graph scale patterns have beenmade by the method of attaching on the panel a transparent plastic boardon which the necessary graph patterns are provided, but recently eitherby one method in which the graph patterns are directly drawn on thepanel surface before complishing a glass bulb consisting of a Panel partand a Funnel part or by another method of forming the necessary graphscale patterns on the inner surface of the panel by light exposure anddevelopment means well known to the CRT manufacturers. In the above, thelatter is preferred above all owing to its lower cost and the advantagein recycling the glass bulb.

One recent method frequently used by CRT manufacturers is as follows:

The inside of a glass bulb, which is arranged so that its panel part isdownward, is filled with a slurry comprising suitable pigment, water,photo-sensitive agents and so on. Negative mask(M), a film on which anegative graph scale patterns 1' are provided for example as shown inFIG. 2, is arranged outside the panel part in parallel to the panelpart. Then, the necessary graph scale patterns are obtained by exposingand developing the slurry precipitates deposited on the inner surface ofthe panel part of the bulb by the light from a light source.

The above-mentioned method has the problems as follows;

1. The mercury lamp generally used in this method does not providemonochromatic light beams but provides light beams of variouswavelengths. Therefore, it is difficult to obtain correct graph scalepatterns since the refractive index of the light beams passing throughthe collimating lens means are different from each other.

2. The light is likely to disperse when it passes through the lens meanssince the lamp is not a point-light source but is a surface-lightsource.

3. The light also disperses due to the ununiformity of the quality ofthe lens means themselves and the intensity of light drops due to thelight transmissivity of each of the lens means.

4. The distance from the light source to the panel gets too far since alarge number of lens means should be used in order to get correctcollimating light beams. As a result, the intensity of the light issignificantly reduced when it reaches the slurry precipitates.

In the above, if the graph scale patterns made without the lens means soas to solve the above-mentioned problems involved in using them, theobtained graph scale patterns may be different from the intended onesbecause of the odds of the incident angles of light arrived at eachposition of the mask and the panel. Also the ideal pattern lines with auniform thickness can not be obtained due to the odds of the intensityof light arriving at each parts of the panel.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved methodthat can effectively solve the problems mentioned above in forming graphscale patterns on the panel of a CRT, particularly to provide a methodwith the outstanding feature and benefit of being able to make the idealgraph scale patterns as required using a specific filter means asdescribed hereinafter.

To accomplish the object of the present invention, there is provided amethod for forming graph scale patterns on the panel of a CRT foroscilloscope comprising the steps of exposing and developing the slurryprecipitates deposited on the inner surface of the panel with the lightfrom a light source passing through a mask film which has the negativeof the graph scale patterns to be formed, a glass plate and the panel,characterized in that a specific filter is used whose lighttransmissivity gets larger along from its center to its peripheralportions. Preferably, the light transmissivity of the filter is about62% at the center portion of the filter. Preferably, the size of thenegative graph scale patterns on the mask is about 94.5-95% of that ofthe real graph scale patterns to be formed on the panel.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and advantages of the present invention will be moreclearly understood through the following descriptions on a preferredembodiment thereof with reference to the accompanied drawings in which:

FIG. 1 is a front view of the CRT panel on which the graph scalespatterns are formed;

FIG. 2 is a front view of a mask having a negative of the graph scalepatterns to be formed;

FIG. 3(a) is a schemetic diagram describing the construction of aexposure system for carrying out the method of the present invention;

FIG. 3(b) is a schemetic diagram describing the construction of aexposure system used in the prior art;

FIG. 4 is a graph showing the incident angle of light on the panel andthe ejective angle of light arriving at the inner surface of the panel;

FIG. 5 is a graph showing the gaps between the graph scale lines formedon the panel and the values of the designed scales on the mask;

FIG. 6 is a diagram describing the theoretical background of FIG. 4 andFIG. 5;

FIG. 7 is a graph showing the variation of the light transmisivity ofthe panel from its center to its peripheral portions;

FIG. 8 is a graph showing the illuminance at each selected position onthe panel after and before using the filter according to the presentinvention;

FIG. 9 is a diagram showing the selected positions on the panel formeasuring from which FIG. 8 and FIG. 10 results; and

FIG. 10 is a graph showing the thickness of scale lines formed at eachposition on the panel before and after using the filter according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The best embodiment of the present invention for desirably achieving thenoted object will be discussed in detail with reference to theaccompanying drawings. FIG. 3(a) is a schemetic view showing the systemfor carrying out the method according to the present invention and FIG.3(b) is a schemetic view showing the system for carting out theconventional method.

As well understood from FIG. 3(b), the conventional method for forminggraph scale patterns on the panel of a CRT comprises the step ofarranging a Glass Bulb(B) filled with a slurry 3 which is material usedfor forming the graph scale patterns on a supporting glass plate 4b, amask(Mb) on which the negative of the required graph scale patterns areformed, a plurality of collimating lens means 5 and a light source 6,the step of exposing the slurry precipitates deposited on the innersurface of the panel (P) to the light passed through the lens means 5,the mask(Mb), the glass plate 4b and the panel (P) in order from thelight source 6, and the step of developing. This method has manyproblems as previously mentioned.

On the other hand, according to the method of the present invention, asshown in FIG. 3(a), the mask(Mb) used in the above conventional methodis replaced with a mask(Ma) having the reduced negative of the graphscale patterns to be formed, the size of which is about 95% of that ofthe real graph scale patterns to be formed on the panel, and a specificfilter 7 is placed between the mask(M a) and the light source 6. Withthe above, the construction of the concerned system can be simplified,and the intensity of light scarcely drops and the light scarcelydisperses because the distance between the panel (P) part of glassbulb(B) and the light source 6 become much shorter. And thus, the bestforming of the required graph scale patterns are obtained.

Additionally, by the present invention, the thickness of supportingglass plate 4a on which the Bulb(B) is placed may be advantageouslyreduced to minimize the refractive index of the glass plate 4a and tomaximize the light transmissivity of the glass plate.

As one of the research steps for achieving the method of the presentinvention, the incident angle of light according to the distance betweeneach graph scale (as shown in FIG. 1) from the panel center at anexposure system which properly set without filter 7 or lens means 5 andthe refractive angle of light arriving at the inner surface of the panelfrom mask hole are measured. A graph in FIG. 4 shows the measuredresult. Here, 1 is a line showing the incident angle of light at eachposition on panel according to the panel scale distance on the basis ofthe panel center and 2 is a line showing the refractive angle passingglass plate from mask hole.

Also, FIG. 5 is a graph showing the measured result of the differencebetween practical graph scales drawn on panel and that designed on themask. Here, 3 is a line showing the design distance of mask scaleaccording to each scale position at the center of panel and 4 is a lineshowing the scale distance drawn on practical panel. And the differencebetween values of said two distances is defined as.

Next, referring to FIG. 6 the theoretical background on FIG. 4, FIG. 5and Table 1 will be discussed. The light emitting from the light sourceis refracted on arriving at the mask surface. Calculating thedisplacement by Snell's rule, it is as follows;

    n.sub.0 SINα.sub.n =n.sub.1 SINβ.sub.n

    Δl=γ.sub.2 tanβ.sub.n

Wherein, n₀ indicates the refractive index of air(n₀ =1), n₁ therefractive index of glass (n₁ =1.5), γ₁ the distance from light sourceto mask (here 105 mm), γ₂ the distance from mask to the inner surface ofpanel (here 10 mm), X'_(n) the distance from the mask center designed,X_(n) the distance from the center of graph scale drawn in the innersurface of panel, α_(n) the incident angle to mask hole from lightsource, β_(n) the incident angle from mask hole to the inside surface ofpanel, Δl the difference between designed values of mask and the scaledistance drawn at the inner surface of panel and l_(n) the theoreticalspace of each scale drawn at the inner surface of panel.

Next, Table 1 below has been derived as a result of measuring each valueof the above defined values at a position corresponding to each scale onpanel when using 1:1 mask.

                  TABLE 1                                                         ______________________________________                                                POSITION (n)                                                          ITEM  UNIT    1        2     3      4     5                                   ______________________________________                                        X'n   mm      10.000   20.000                                                                              30.000 40.000                                                                              50.000                              Xn    mm      10.633   21.275                                                                              31.863 42.443                                                                              52.992                              αn                                                                            deg     5.44     10.78 15.95  20.85 25.46                               βn                                                                             deg     3.62     7.17  10.55  13.73 16.66                               Δln                                                                           mm      0.633    1.257 1.863  2.443 2.992                               ln    mm      10.633   10.624                                                                              10.606 10.508                                                                              10.549                              ______________________________________                                    

As seen from the result of the above Table 1, the scale has not beenmade in the range of standard tolerance because the tolerance of scale(judging by l_(n) values) went off the standard tolerance 10+0.08.

And as the result of using the reduced mask of 94.5%, the scale can bemade in the range of the above standard tolerance as shown in belowTable 2, and using the reduced mask of 95%, the scale can be formed inthe range enough allowable tolerance as shown in below Table 3 andconventional exposure time of 3-5 minutes can be greatly reduced up to30-60 seconds owing to light quantity increased by reducing exposuredistance more than 50% of that when using lens means 5.

                  TABLE 2                                                         ______________________________________                                        the scale spaces drawn on the panel when using the reduced                    mask of 94.5%                                                                 POSITION (n)                                                                            1         2       3       4    5                                    ______________________________________                                        SPACE (mm)                                                                              10.048    10.039  10.02   9.998                                                                              9.985                                ______________________________________                                    

                                      TABLE 3                                     __________________________________________________________________________    the values measured practically of scale drawn on the panel when              using the reduced mask of 94.5% (unit mm)                                              VALUES OF ALL SCALES                                                                         VALUES OF EACH SCALE                                           PRACTICAL      PRACTICAL                                             ITEM     PART    STANDARD                                                                             PART    STANDARD                                                                             etc                                    __________________________________________________________________________    HORIZONTAL                                                                             99.66   100 + 0.8                                                                            Max: 10.04                                                                            10 + 0.08                                     PART                    Min: 9.98                                             VERTICAL 79.68    80 + 0.6                                                                            Max: 01.03                                                                            10 + 0.08                                     PART                    Min: 9.99                                             __________________________________________________________________________

However, in the extension exposure method not using lens, the thicknessof scale being exposed and developed at the inner surface of the panelis not uniform because the difference of each light quantity arrived istoo big at the edge and center of the panel if the exposure distance isshort.

In order to cope with the above problem in the present invention, aspecific filter as explained below has been used.

First, FIG. 7 is a graph describing the variation of transmission factorof light from the panel center receiving the light emitted from onelight source to the edge, wherein 5 and 6 indicate the line oftransmission factor in inverse function and infunction, respectively.The theoretical principle and general equation for seeking transmissionfactor and illuminance according to the distance variation from thecenter are as follows; ##STR1##

In above case, when γ=115 mm, l=70 mm, the light quantity at the paneledge is Bq/Bp=0.62, that is, 62% of the light quantity of the panelcenter. Accordingly, if the light quantity of the panel center isreduced to 62% by using the specific filter so as to compensate this,the light quantity of all surface of the panel can be controlleduniformly.

Suppose the relation between the transmission factor of filter and theilluminance of panel is inverse function, the transmission factor ofeach scale distance from the panel center becomes the result as shown inFIG. 4.

In first, the illuminance equation of panel is as follows; ##EQU1##

The equation for yielding the transmission factor is as follows;##EQU2##

Therefore

when l=0 (center), T(l)=62(%)

when l=7 cm, T(l)=100(%), and

a general equation of transmission factor T(l)=0.0413(11.5+l²)^(3/2)=0.8 is obtained.

                  TABLE 4                                                         ______________________________________                                        THE DISTANCE FROM                                                                             0     1     2   3   4   5   6   7                             THE CENTER 1 (on)                                                             TRANSMISSION   62    63    65  69  74  81  89  100                            FACTOR (%)                                                                    ______________________________________                                    

Next, FIG. 8 is a graph describing the illuminance after and beforeusing the filter (as shown in FIG. 3) having the transmission factor ofwhich is 62% in the center and becomes larger at the edge, wherein 7indicates the illuminance before using the said filter, 8 theilluminance after using the filter. The illuminance measured at eachposition on the panel in FIG. 9 is shown in Table 5.

                                      TABLE 5                                     __________________________________________________________________________    (unit: mw/cm)                                                                                POSITION                                                       ITEM           CENTER                                                                              1  2  3  4  5  6  7  8                                   __________________________________________________________________________    ILLUMINANCE    0.76  0.55                                                                             0.52                                                                             0.52                                                                             0.50                                                                             0.46                                                                             0.45                                                                             0.45                                                                             0.45                                (BEFORE USING-FILTER)                                                         IILUMINANCE    0.39  0.40                                                                             0.41                                                                             0.40                                                                             0.39                                                                             0.40                                                                             0.40                                                                             0.41                                                                             0.41                                (AFTER USING FILTER)                                                          __________________________________________________________________________

Therefore, the (measured) result of measure shows the illuminance ofeach position on the panel is almost regular when using the filter ofwhich the center transmission is 62%.

Next, FIG. 10 is a graph describing the thickness of lines developed ateach position on the panel shown in FIG. 9 after and before using thefilter, wherein 9 and 10 indicate the line describing the thickness ofline developed at the panel before using the filter and when using thefilter, respectively, The below Table 6 is the result confirming thethickness of the scale lines in case exposure time is minute and thecenter illuminance is 0.40 mw/cm².

                                      TABLE 6                                     __________________________________________________________________________    The thickness of line before and after using the filter (unit: mm)                           POSITION                                                       ITEM           CENTER                                                                              1  2  3  4  5  6  7  8                                   __________________________________________________________________________    THICKNESS      0.32  0.28                                                                             0.25                                                                             0.26                                                                             0.24                                                                             0.18                                                                             0.21                                                                             0.19                                                                             0.20                                (BEFORE USING FILTER)                                                         THICKNESS      0.20  0.19                                                                             0.19                                                                             0.20                                                                             0.21                                                                             0.19                                                                             0.20                                                                             0.20                                                                             0.20                                (AFTER USING FILTER)                                                          __________________________________________________________________________

From Table 6, we can know the facts as follows;

The thickness of scale lines on the panel exposed and developed by thearrangement of FIG. 3(a) using the filter whose light transmissivity atits center is about is 62% satisfies the allowable condition in thestandard tolerence of 0.2+0.05 mm with maintaining almost uniformthickness at all positions from the center to the edge. On the contrary,in case the filter is not used the thickness difference of scale lineson the panel is too large, so that it is not possible to apply it to theproduct. Moreover, the difference the shorter exposure time or the lowerthe illuminance, the larger.

The method according to the present invention making use of exposuresystem including the filter means can be very profitably applied notonly to the case mentioned above but also to any exposure system needingcollimating light beams.

As well understood from the above description, the method according tothe present invention for forming graph scale patterns on the panel of aCRT for osciloscope has the following advantages, that is, the distancebetween the panel and the light source can be drastically reduced byusing a specific filter instead of using several collimating lens meanswhich have been used in the conventional methods, the overall exposureconstruction of the concerned system can be greatly simplified, and thebest forming of the intended graph scale patterns can be obtained.

What is claimed is:
 1. A method for forming graph scales on the panel ofa cathode-ray tube panel for an oscilloscope comprising the steps ofarranging a glass bulb (B) filled with a slurry (3), a glass plate (4a)for supporting said bulb (B), a mask (Ma) having a negative of the graphscale to be formed on the inner surface of the panel portion (P) of saidbulb (B), and a light source (6) in the required order; forming thegraph scale on the inner surface of the panel portion (P) of said bulb(B) by exposing and developing the slurry precipitate on the innersurface of the panel portion (P) by means of the light directed theretofrom said light source (6) through the mask (Ma), the glass plate (4a)and the panel portion (P), and arranging a filter (7) whose lighttransmissivity increases from its center to its peripheral portionsbetween said mask (Ma) and said light source (6).
 2. The methodaccording to claim 1, wherein said mask (Ma) has the negative of thegraph scale with a size about 94.5-95% of that of the graph scale to beformed on the panel portion (P).
 3. The method according to claim 1,wherein the light transmissivity at the center of said filter (7) isabout 62%.